Purging compounds have been used to clean out an extruder of molten resin for product changeover, for example from a specific resin dyed of one colour to the same resin in another colour, or from a resin of one chemical composition to a second resin of a different chemical composition.
The transition from a polar to a non-polar resin, as from nylon to polyethylene, presents a number of practical problems.
Nylon type resins, owing to their polar characteristics, have a strong affinity for metals in the extruder thus making it very difficult to clean the extruder in a reasonable time before transitioning to Polyethylene. This can result in a significant downtime thereby resulting in loss of productivity and higher cost for the manufacturer of films (converter).
Botros in his paper (ANTEC 1996) had described the use of a Purge compound, Plexar 909, an anhydride modified LDPE to purge polar resins from co-extrusion equipment. Botros describes the use of analytical techniques such as Intec Gel Analysis, Optical microscopy and FTIR to evaluate the purging efficiency.
In the Journal of Plastic Sheeting and Paper (Vol. 12, No. 3, 212-224, 1996), Botros describes the use of Plexar 909 to purge Polyamides and Ethylene Vinyl alcohol type polymers from the extruder.
U.S. Pat. No. 6,022,420 describes the use of a fluoropolymer to purge thermoplastic resins from the extruder.
U.S. Pat. No. 3,869,525 describes the use of a mixture of thermoplastic polymers, consisting of Polyethylene and Polyester for cleaning or purging the extruder.
U.S. Pat. No. 4,731,126 describes the use of thermoplastic polymers with hydroxymethyl-substituted carboxylic acids for purging polymeric residues.
U.S. Pat. No. 7,479,327 refers to the use of tie layer materials with ionomer-based films and sheets as skins on other materials.
A number of products are commercially available from chemical companies for use in the purging from extruders of more complex compounds, such as engineered thermoplastics, exemplified by the “Rapid Purge” purging compounds from Rapid Purge Chemical Company for purging resins such as EVAOH, EVA, Polyethylene.
A need exists for a purging compound which can effect a smooth transition of relatively short duration from polar to non-polar thermoplastics, particularly from polyamides such as Nylon-6 to polyethylene based films.